SPN 846 FMI 0Transmission
Transmission Fluid Pressure Sensor/Switch A Circuit
Scan Tool — in guided session
DVOM Testing — in guided session
Connector Pinout — in guided session
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Overview
Fault Code
SPN 846 / FMI 0
Category
Transmission
Derate Risk
No
Regen Inhibit
No
Inducement Risk
No
Component Location: The transmission fluid pressure sensor is typically mounted on the transmission case, often near the valve body or control module.
Common Symptoms
- Check engine light or malfunction indicator lamp illuminated
- Transmission derate or reduced power mode
- Harsh or delayed shifts
- Transmission fails to shift properly
- Limp mode activated
Root Causes
- Faulty transmission fluid pressure sensor Low transmission fluid level Damaged wiring harness to pressure sensor Corroded or loose sensor connector Internal transmission fluid pressure issues
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Derate Behavior
Power Derate
No
System Interactions
SPN 846 FMI 0 interacts with the following systems and may trigger cascading faults if not resolved promptly.
Common Diagnostic Mistakes
Replacing the sensor without verifying wiring continuity and supply voltage first.
Clearing codes without identifying and resolving the root cause — the fault will return.
Ignoring related active faults — cascading faults often share a root cause.
Skipping the connector inspection — corrosion and damaged pins are a leading cause of sensor faults.
Condemning the ECM before exhausting all wiring and component tests.
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OEM System Resources
ASE Training Resources
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Related Diagnostic Articles
Deep-dive diagnostic page: SPN 846 FMI 0 — Full FSM Sequence & Repair Steps — includes wiring notes, sensor specs, and gated repair procedures.
Authority References
Diagnostic procedures on this page are informed by OEM service literature and industry standards.
Cummins QuickServe OnlineOfficial Cummins service manuals, fault code lookup, and TSB database.Detroit Diesel DiagnoCentralDetroit Diesel diagnostic procedures, DDDL documentation, and service literature.PACCAR MX Engine ServicePACCAR MX-11 and MX-13 engine service documentation and DAVIE diagnostic guides.Volvo/Mack Tech ToolVolvo and Mack engine fault code reference and PTT/Tech Tool diagnostic procedures.ASE — Diesel Truck Technician CertificationNational Institute for Automotive Service Excellence — T2 Diesel Engines certification standards.EPA Aftertreatment & Emissions GuidelinesU.S. EPA heavy-duty diesel aftertreatment compliance, DPF/SCR regulations, and NOx standards.
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